The invention relates to a process for the recycling of rigid polyurethane foam and the production of molded pieces of pretreated rigid foam by comminuting the starting product to &lt;10 mm, mixing it with a binder (polyurethane adhesive) and pressing it at temperatures between 100.degree. and 200.degree. C. and a pressure of up to 20N/mm.sup.2. The invention relates also to an installation for processing the rigid polyurethane foam, comprising a mill, a sizing screen, a mixing device, and a press.
In a known process of this type (Japanese Application 57-34926 and French Application 20 29 622), material for packaging and insulation purposes is produced from the particles of a rigid polyurethane foam and a binder. These particles are comminuted suitably to below 20 or 10 mm, mixed with the binder, and are then compressed in a heated press, and the boards thus obtained are used as a thermally insulating material. These boards are, however, not elastic and break-resistant enough to use as boards per se, but at most can be used as a substitute for rock wool or similar mats. East German Patent 144 885 introduces a process for producing molded pieces of polyurethane foam waste wherein comminuted polyurethane foam waste with a particle size between 0.5 mm and 10 mm diameter are moistened with a rubber solution. This starting material is used to produce boards, coatings, and other molded pieces. It is also known (from German Patent 24 39 672) that flexible floor covering boards are produced by plastifying shredded synthetic leather waste and other comminuted materials of thermoplastic synthetic material in an extruder and to produce from the material processed in this manner, by way of a press device, a web that is then cut into individual boards. In another known process, non-slipping coating material is produced from a mixture of integral foam granulate, flakes, and soft polyurethane foam in a heated press at approximately 190.degree. to 200.degree. C. (East German Patent 114 927). The soft polyurethane foam flakes hereby function as a binder.
Finally, German Patent 38 44 664 reveals that the material is first compressed with low pressure in a two-step process from suitably comminuted polyurethane foam and a binder, and that this material is then finished by compression in a second step with a higher pressure (4N/mm.sup.2). The boards manufactured in this manner supposedly are superior to particle boards in terms of elasticity and breaking resistance. A disadvantage, however, is that this process essentially presupposed clean production waste. It was also found that comminution to 20 mm and below, i.e. to approximately 10 mm, is insufficient for performing the process without any problems. It is particularly disadvantageous that the process requires discontinuous steps, since the press must be stopped for some time after reaching the end of the compression path before the pressure can be released and the material is unmolded. The output of an installation working according to this described process is thus limited.